The present invention relates to an improved method for recovering vanadium from residues from the combustion of petroleum fractions, in particular heavy fractions of petroleum.
The addition of magnesium oxide in the combustion of petroleum derivates or fractions, in particular heavy fractions, is now generally employed in thermoelectric power plants since it preserves the plant from corrosion, by lowering the acidity of the flue gases, for a much longer time.
Consequently, for those crude oils which naturally contain very little iron, the presence of iron in the solid residues of combustion (ash and soot) has been considerably decreased, since the part thereof originating from corrosion has been eliminated. It is not infrequent (though this is not always the case) to find iron contents below 1% in the ash of the electric filters of power plants powered by fuel oil, this being a great advantage for the recovery of vanadium from this ash, with respect whereto iron is in one manner or another an interfering element.
The methods of the prior art for recovering vanadium from the residues of petroleum combustion, even when such residues had the above described low iron concentrations, of 1% or less, required a previous separation of this cation; this because the latter, even when it is present at trace levels, interferes with the vanadium precipitation process, making it incomplete.
This preliminary separation step obviously entailed hardly negligible burdens on the process and plant costs.